The present invention is directed to so-called picket or zig-zag type heater elements employed in high temperature furnaces of the type, for example, used in crystal growing processes. (For examples of furnaces of this type, see U.S. Pat. Nos. 2,650,254; 2,966,537; 3,359,077 and 3,798,077.)
The picket type heating element employed in such furnaces is in the form of a cylindrical shell which surrounds the crucible holding the material to be critically heated. The heater conventionally is machined from a graphite composition into a cylindrical shape with relatively long axially extending slots extending alternately from opposite ends of the cylindrical shell at uniform spacing to each other to provide the "zig-zag" current path.
Particularly in crystal growing operations, the temperatures produced by the heating element must be not only relatively high temperatures, but also extremely uniform in terms of the application of heat to the crucible. Because the element operates as an electrical resistance heater, the heat produced at any given location is directly proportional to the cross-sectional area of current flow. While it is possible to form and machine the heating elements with the necessary degree of precision, the completed graphite heating element is quite brittle and subject to cracking or chipping, even when extreme care is used in handling and cleaning the element. Because a relatively small crack or chip can have an unacceptably deleterious effect upon the uniformity of heating produced by the element, such heating elements, which are very expensive, require frequent replacement.
The present invention is especially directed to a method of making a segmented heater without adversely affecting the heat distribution of the assembled elements.